25% of the Universe that we can’t possibly see!
In the last story where I stated that Einstein’s theories couldn’t explain the existence of Dark Matter and neither do any of the theories till date. This doesn’t mean that Einstein was completely wrong but his theories weren’t precisely correct either. Refer to this story to know why Einstein or Newton wasn’t either right or wrong: https://medium.com/@lakshyapratapmonga/and-now-einstein-was-wrong-35b07d567c1e
Imagine you are standing under a waterfall and the water doesn’t hit you at all. Instead the water keeps passing right through you all the time. You don’t get wet. It feels like the water is not at all there. But the catch here is, you can see the water and you can see the lake. The question here is, why does the water keep passing right through you?
In the cosmic nature of our universe, Dark Matter is something that you can relate to that has the inability to interact with matter that comprises us and being seen by the best of the detectors (telescopes, chemical reactions, spectroscopes, particle detectors/accelerators etc.) ever engineered. Termed on the basis of the nature of interaction, Physicists agreed upon a name to call these unknown particles which comprises Dark Matter: WIMPs, Weakly Interacting Massive Particles.
As described earlier, these particles don’t interact with the particles that currently exist in the Standard Model of Elementary Particle.
Particles in the Standard Model make up the 5% of the entire universe currently known to us.
Also termed as Baryonic Matter which humans and our instruments can interact with (stars, planets, moons, asteroids/comets/meteors, intergalactic gas, black holes).
Commonly we label matter interactable on the basis of its interaction with Electromagnetic Radiation. The ones which don’t interact at all are categorized as: Dark Matter, Dark Energy and Neutrinos (the interaction has to be induced rather that direct).
WIMPs can be categorized under one more category, non-baryonic particle, simply which don’t exist in the Standard Model, currently. In the field of Cosmology, studying the history of the universe gives a notion that WIMPs existed since the dawn of the universe as we know it, 13.8 Billion years ago, even before Baryonic Matter was a thing.
It was responsible for the formation of the first galaxies, first stars, superclusters and galactic neighborhoods. Why? Just because of the simple physical law that Newton stated:
Irrespective of the nature of matter, it would attract other matter proportional to its mass and distance.
Dark Matter attracted Baryonic Matter, forming small globule like structures. These structures comprised only of the first two elements of the Periodic Table of Chemical Elements, Hydrogen being the dominating one. These globule like structures were what we today call “Stars”.
What happened to the WIMPs/Dark Matter?
Formation of Stars induced the formation of Galaxies. Mere stars couldn’t form galaxies all by themselves. Dark Matter being 5 times more than Baryonic swooped into the story again. Stars lacked the Gravitational Strength to attract enough Stars/Planets/Intergalactic Dust to form an entire galaxy.
Dark Matter was the one which induced more Gravitational Strength. WIMPs provided the the appropriate magnitude of Gravitational Force due to its massive nature, Galaxies were inevitably formed. With similar activity, Local Neighborhoods were formed along with Galactic Clusters and Superclusters. Indicating one more fact that Dark Matter’s existence 5 times more than Baryonic Matter is what drove the formation of the celestial bodies.
Partly responsible for the formation of what we today perceive as our Cosmos, we still couldn’t trace its existence. Its existence can be seen in the Cosmic Microwave Background all over the sky in all directions. The anisotropies -inconsistencies — in the CMB does indicate the existence of Dark Matter indeed.
The indication points out that Dark Matter was a significant part of our Universe’s history and exists all around us.
How are we still sure that Dark Matter, is.. Matter?
Matter is what makes things up, Light is what enables us to see it. Pretty straightforward, isn’t it? Question is what makes matter, matter and light, …light?
Density isn’t an unheard term. Radiation Density is something that is unheard of. We have used Mass Density in our high school calculations but Radiation Density doesn’t make to much discussions. Both of them are radically distinct.
Radiation Density doesn’t equate to Radiation/Volume contrast to Mass Density which equates to Mass/Volume.
Allow me to clarify with the help of an analogy. By chance, you have an empty cubical box. It’s filled with air with density [ρ]. Mass of the air would remain constant opposed to pressure & density which would vary. Now expand the box so that the side of the cubical box is twice than before. What would be the new density of the gas?
The density of the gas would be [ρ/8]. It would decrease 8 times which is mathematically the cube of 2.
It indicates that the density of matter would decrease/increase inversely proportional to the volume of the container (x³ in case of a cube)
Radiation Density doesn’t quite agree to this mathematics. The latter holds inverse proportionality for the biquadrate of the side of the container. What if the container’s not a cube which doesn’t hold the property of homogeneous sides?
Radiation Density ∝ 1/a⁴
Answered with simplicity, Radiation can’t be contained, the parameter can only be measured indirectly though detectors and assistance of mathematical equations. For the betterment, allow me to continue the analogy.
In the case of mass/matter, the density reduction was by 8 if the side of the cubical container doubled. Radiation Density would reduce 16 times on the same parametric change. See the difference now? The change would follow the order of 4 when Radiation comes into play.
Dark Matter agrees with the mathematics of matter. As per the observations and further mathematical development, the indication clearly points towards the change on the order of 3 in case of Dark Matter. If the same wouldn’t agree upon the former, it would rather be the advent of Distinct Manifestations of Space-Time other than Mass and Energy contrasting to the advent of Dark Matter.
At least for the time being we know that Dark Matter is:
- Undetectable (Weakly Interacting): Interaction with Baryonic Matter or Electromagnetic Radiation seems incompatible for Dark Matter
- Massive : having mass and being categorized as Matter instead of energy/radiation
- Quantified (Particles): existing in the form of particles at the smallest scale
Based on these three main properties of Dark Matter, the most well accepted theory indicated the existence of Weakly Interacting Massive Particles OR WIMPs.
This was the Dark Matter’s unpopular role in our Universe simply explained!
What are the physical properties of WIMPs, what are the alternative physics descriptions of Dark Matter that fit into the current Cosmological Model, are there exceptions to this theory, what makes it more certain that the Dark Matter theory is more suitable than other explanations of gravity?
The answer to these questions you may find in the next story, or you curiosity!!
Thanks for reading till here, awesomely high-five 🙌🙌. Have a great day ahead!!
